Are you talking about Jono? Jono is a chatbot that was installed by Kiros. It messes up the chat and was formerly known as 'VirtualTeen' (he appeared after the site was hacked in 2006). This chatbot was very very annoying and messed up the chat for everyone (slowed it down, made bad connection problems etc) and was removed.
Evidently, Kiros decided to re-install it (after he updated the site to vB 3.6.7, I saw him alone in the chat for a few minutes) and renamed it.
So in conclusion, this is not a ghost member or a hacker, since he does not appear on the 'Who's In Chat' list at the bottom of the index. He is part of the chat!
edit: P.S.: after I found out about Jono and noticed that he was a chatbot (did this 2 days ago), I logged out. Now I can't get into chat - it won't recognize my login info